Answer:
Some of the problems you face when listening to a lecture
Firstly, how much noise is actually being made by the lecturers? Is it loud enough to be heard from the back? Is it subtle enough to have to raise your voice to be heard? Is it really loud enough to be heard by everyone?
Secondly, will other people in the room actually hear what is being said? While silence might look glamorous and ideal, it can be distracting and unhelpful to the lecture for a number of reasons.